2.55B Absorption of Water by Root Hair Cells (Edexcel IGCSE Biology)

Uptake of water into the root

• Root hairs are single-celled extensions of epidermis cells in the root
  • They grow between soil particles and absorb water and minerals from the soil
• Root hair cells are adapted for the efficient uptake of water (by osmosis) and mineral ions (by active transport)
  • They contain mitochondria which release energy for active transport
  • Root hairs increase the surface area of plant roots, increasing the rate at which water and minerals can be taken up
• Root hair cells take up mineral ions and water from the soil as follows:
  1. Roots hair cells take up mineral ions from the soil by active transport
  2. The water concentration of the cell cytoplasm is reduced due to the presence of mineral ions 
  3. Water moves into the root hair cell by osmosis

A root hair cell

The structure of a root specifically allows it to maximise absorption of water by osmosis and mineral ions by active transport

The route of water through the plant

• Water moves, by osmosis, into the root hair cells, through the root cortex and into the xylem vessels:
• Once the water gets into the xylem, it is carried up to the leaves where it enters mesophyll cells
• So the pathway is:

root hair cell → root cortex cells → xylem → leaf mesophyll cells

Pathway of water into and across a root

• The pathway can be investigated by placing a plant (like celery) into a beaker of water that has had a stain added to it (food colouring will work well)
• After a few hours, you can see the leaves of the celery turning the same colour as the dyed water, proving that water is being taken up by the celery
• If a cross-section of the celery is cut, only certain areas of the stalk is stained the colour of the water, showing that the water is being carried in specific vessels through the stem - these are the xylem vessels

Investigating water movement in plants using a stain